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Old 07-09-2017, 08:44   #91
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Re: Not another one?

Originally Posted by estarzinger View Post
Dude, practically speaking when offshore watch keeping in order to 'advance his position with DR' you just simply look down the route for (say) 10nm. You don't need to do anything sophisticated or a calculation. And if you are on a plotter (raster or vector) you flick the zoom a bit. None of this takes any time to do. It may look like 'gazing at a plotter' but there is (should be) actually a thought process going on rather than a blank stare and blank mind.

It is in fact one of the advantages of a plotter. You (always) know where you are on the displayed chart and your route/course line. You don't have to plot a position, removing the potential for at least one possible error.
Agreeing with Evans and Stu --

What's the point of doing DR by hand, if you have valid GPS data? And why is this "real navigation", and correctly using GPS data is not?

I still do a lot of traditional navigation, and am considered by many to be a dinosaur, but this seems to me to be really over the top.

DR is a great exercise (and I think all sailors should know how to do it), and it is a valid way to cross-check or back up other position data, if you need to do that, but GPS/Glonass position data is extremely reliable, and I can't imagine how it would be worth diverting time and attention away from other navigational tasks, just to back up or cross check your GPS.

Keep in mind Evans' "triage of focus and attention" -- a really astute phrase in my opinion. This resource -- especially on a short-handed yacht crossing an ocean -- must be used efficiently. If you have a chart plotter, a routine like what Evans described is the most efficient way to check where you are and what is around you and prevent what happened to the poor guy this thread is about. Cross check with eyeballs, radar, and depth sounder. Cross check the electronic chart with, ideally, a paper one, or at least, a different electronic one. When using electronic charts, keep in mind the zoom problem (although that doesn't seem to be what the problem was in this particular case).

But DR, in my humble opinion, is a big waste of time and effort, if you have a working plotter. Much better, in my humble opinion, to spend that time scanning the horizon, or digging into the charts.
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Old 10-09-2017, 00:38   #92
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Re: Not another one?

I have not read the entire thread, but will come back and do so.

I have delivered many a yacht into the Caribbean from the south and taking a route up the island chain to pass Monserrat, leaving the island just to starboard (for the crews to have a look at the volcanic eruption) and heading to Oyster Pond in St Maarten. These were all new catamarans.

When the yard changed to a new Raymarine series plotter with Navionics charts, I had plotted a course and thought that something did not look correct on the display. After going through the plotted course I suddenly realised that Redondo island (just NNW of Monseratt) was missing on the electronic chart.

Zooming in revealed the missing island - my course would have put us going through the centre of the island!

I have always carried paper charts on board, but only as a back-up. Since then I plot on paper and then transfer to plotter, just to be double sure the vessel and crew will have a safe journey as far as not ending up on some real coast that is not fully covered by the digital charts.

A lesson learnt by a mistake that could so easily have ended in disaster.

For those that are wondering, Redondo is now shown clearly at any zoom!
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